Iran Cools Nuclear Work as Vote Looms

WASHINGTON—Supreme Leader Ayatollah Ali Khamenei has decided to keep Iran's nuclear program within limits demanded by Israel for now, according to senior U.S., European and Israeli officials, in a move they believe is designed to avert an international crisis during an Iranian election year.

With a vote set for June, Mr. Khamenei is eager to place a leader more aligned with his positions than current Iranian President Mahmoud Ahmadinejad, without sparking a repeat of the nationwide unrest that followed a 2009 vote, these officials said.

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U.S. and European officials have worried Mr. Khamenei might challenge Israel and the U.S. over the nuclear issue to consolidate his political position. But instead of pressing an agenda that could heighten tensions between Tehran and the international community, the opposite is happening, for the time being, these officials said.

Mr. Khamenei's approach is placing the Obama administration and its allies in a delicate strategic position, possibly constraining their response to Iran's nuclear program. U.S., European and Israeli officials have described 2013 as the "critical" year in Iran's nuclear program, which has been seen as a reference to the possible use of military force.

The U.S. is also facing the threat posed by North Korea's nuclear program, with Washington and Pyongyang engaged in heightened military threats. The North conducted its third nuclear weapons test in February.

International negotiations aimed at containing Iran's nuclear program resume Friday in Kazakhstan and involve the five permanent members of the U.N. Security Council plus Germany. It will likely be the last round of diplomacy with Tehran until after the June elections, U.S. officials believe.

Seeking to ward off international pressure, Iranian nuclear officials have kept the country's stockpile of uranium enriched to 20% purity below 250 kilograms (550 pounds). Iran would need such an amount—if processed further into weapons-grade fuel—to produce one atomic bomb, experts believe. It is also the amount Israeli Prime Minister Benjamin Netanyahu told the United Nations in September that the world should prevent Iran from amassing, through a military strike if necessary.

The U.N.'s nuclear watchdog, the International Atomic Energy Agency, said in late December that Tehran had amassed 232 kilograms of uranium enriched to the 20% level but that almost 100 kilograms of that amount is being converted into fuel plates to power Tehran's research reactor. Fissile material in this form is difficult to use in a weapons program, U.S. and European officials said.

"Based on the latest IAEA report, Iran appears to be limiting its stockpile of 20% enriched uranium by converting a significant portion of it to oxide," said a senior U.S. official working on Iran. "But that could change at any moment."

U.S. and Israeli officials believe Iran's moves represent a delay, rather than a change of heart, and that other actions are accelerating the pace at which the country could create weapons-grade fuel. It has installed thousands of new centrifuge machines at an underground military facility in the holy city of Qom, the IAEA reported. The site, called Fordow, is in a fortified bunker and seen as largely immune to U.S. or Israeli military strikes.

Iran also has been adding advanced centrifuge machines that are seen as capable of tripling the pace at which it enriches uranium. If Mr. Khamenei decides to breach Israel's mark later this year, U.S. and Israeli officials said, Iran could move more rapidly to produce the weapons-grade fuel required for a bomb.

"There is a good point to be made that Iran has accepted 250 kilograms as the red line, but they are doing this very cleverly," said Michael Oren, Israel's ambassador to the U.S., in an interview. The country's moves would "enable Iran to cross the red line clandestinely in a matter of weeks," he said.

Iran has repeatedly denied it is seeking a bomb and has said it is developing only a civilian nuclear-power program.

The issue of Iran's nuclear program continues to dominate relations between the U.S. and Israel and was a primary topic of discussion when President Barack Obama met with Mr. Netanyahu in Israel last month, said U.S. and Israeli officials.

In Jerusalem, Mr. Obama said he believed Iran would need a year to make a nuclear weapon if Mr. Khamenei made the political decision. Mr. Netanyahu didn't dispute that. But Israeli officials are worried Tehran is rapidly approaching a point at which its nuclear-fuel production sites can no longer be removed through military action—a so-called zone of immunity.

U.S. and European officials taking part in the diplomacy with Iran this week in Almaty said the focus will again be to get Tehran to cease its production of 20%-enriched uranium and agree to ship out a sizable portion of its stockpile to a third country.

This approach is seen as limiting Iran's ability to quickly attempt to produce nuclear weapons. In return, the U.S. and its diplomatic partners will offer to reduce some of the economic sanctions imposed on Tehran in recent years, including a ban on its trade of gold and precious metals, said officials involved in the diplomacy.

U.S. officials are doubtful of any major breakthrough in Kazakhstan, in part because of Mr. Khamenei's fixation on the June elections. The 73-year-old cleric is the ultimate decision maker on Iran's diplomacy and nuclear program, according to Iranian officials. His personal representative, Saeed Jalili, will lead Tehran's negotiating team in Kazakhstan.

Mr. Khamenei initially was a supporter of Mr. Ahmadinejad, including during 2009 presidential elections that the opposition claims were rigged. Mr. Ahmadinejad's disputed re-election brought millions of protesters onto Iran's streets and posed the greatest threat to the stability of the Islamic Republic in decades.

Mr. Khamenei, however, is believed to have grown wary of the outspoken Iranian president, whose second and final term is ending. Mr. Ahmadinejad has challenged many in Tehran's political elite and exacerbated Iran's economic ills by spending lavishly on populist development projects.

Mr. Ahmadinejad has been a staunch defender of Iran's nuclear program but has also shown a willingness to negotiate, U.S. and European officials said. In late 2009, Tehran initially agreed with world powers to a deal to ship out the majority of its enriched uranium to a third country, in diplomacy that was seen as backed by Iran's president. The pact fell apart, though, after Mr. Khamenei ruled against it, these officials said—a signal of Mr. Ahmadinejad's limited power.

The supreme leader is seeking a more malleable replacement for Mr. Ahmadinejad, according to political analysts—potentially Mr. Jalili.

Iran's supreme leader has regularly voiced opposition to bilateral talks with Washington on the nuclear issue. He has historically said giving ground on the nuclear question could only embolden the opponents of the Islamic Republic to seek regime change, and his orientation toward the red line could be reversed after the election.

"The supreme leader might feel he's in a stronger position as far as the next steps in the nuclear program," said Gary Samore, who was Mr. Obama's top adviser on nuclear issues during his first term. "You could imagine, later this year, a confrontation."

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